U.S. Pat. No. 5,036,534 (the specification of which is incorporated herein by reference, and referred to henceforth as "the prior application") presents methods and apparatus to enable a telephone subscriber to utilize a plurality of previously incompatible telephone device systems on the same telephone line. This is accomplished by allowing a first device system to respond to an incoming telephone call, while monitoring the telephone line to detect various modes of operation of the first device system and to detect an off-mode condition not corresponding to a mode of operation of the first device system; thereupon establishing communication between a second device system and the telephone line, and so forth. In the specific embodiments of the invention discussed within that specification, much of the monitoring functions are effected through analog circuitry, that convert the various signals on the telephone line into a plurality of logical condition signals that are subsequently used by a high-level decision and control microcomputer to carry out the algorithms discussed therein. The instant application, while continuing the general decision and control algorithms of the earlier application, includes specific improvements on the low-level monitoring and control functions disclosed therein. In particular, portions of the monitoring circuitry have been replaced by digital signal processing in such a way as to reliably and effectively convert the various waveforms into logical condition signals. Also, the ring-trip circuitry used to actuate the second (and subsequent) telephone device systems is further streamlined for improved performance. Many of the improvements presented herein may also be of use in other communications applications than just the specific intelligent interface described herein.
Therefore, an object of this invention is to enable any of a large selection of otherwise incompatible communication device systems to be utilized with the same communication line in such a manner as to ensure harmonious operation of each of the systems, through digital signal processing techniques.
Another object of this invention is to enable a communications system to have portions of its analog monitoring circuitry replaced with digital signal processing while maintaining or improving the performance of the system.
Another object of this invention is to develop communication monitoring circuitry and software as subsystems capable of wide applications beyond just the specific applications relating to intelligent telephone interfaces.
These and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings and the specification of the copending application referenced above.